1. Field of the Invention
The present invention relates to the technical section of operation and application of differentials used in all types of wheeled vehicles. The present invention concerns differentials such as employed in connection with drive axles for motor vehicles.
2. Brief Description of the Background of the Invention Including Prior Art
A double-shuttle motion transmitting apparatus is taught in U.S. Pat. No. 4,291,591. A differential action between shaft members is provided by oscillation and reciprocation of the shuttle members in opposite directions relative to another axis disposed perpendicular to the shaft axis.
The U.S. Pat. No. 3,548,683 teaches a differential gear mechanism with wobbling inertia ring. A wobbling ring gear is disposed between two side gears in driving engagement therewith to develop an inertia torque bias for delivering torque to each of the two side gears carried by axially aligned power output shafts.
The International Patent WO 88/05139 teaches a nutating gear positraction or non-slip differential, which allows two shafts or wheels to rotate at different speeds, with one shaft or wheel faster than the other shaft or wheel. Two cam-operated nutating gear sets are employed in the gear and each axle or shaft is connected to the cams of the gear sets respectively.
In case of a conventional differential, it is well known that the sum of the speed on both wheels attached to the two sides of the differential is constant under a specific number of revolutions per minute of the engine. The sum of the speeds of two wheels of a conventional differential is directly proportional to the rotation speed of the motor shaft. Consequently, when both driving wheels are in traction on the pavement, with a different coefficient of friction .mu., then one wheel will accelerate and the other will decelerate with the well known undesirable effects. The one wheel with the lower adhesion or traction will spin, whereas the other wheel does not turn at all.
Under these conditions, the power transmitted by friction forces of the differential on both wheels is minimal and the vehicle is brought to a standstill (FIG. 7). When the wheel lacking traction spins, the wheel with traction will stop and therewith the whole motor vehicle will stop.
To overcome this difficulty, various differential types of limited slip were developed, which aim at improving the adhesion, with the variation of torque distribution, on the wheel with the greatest adhesion. While the conventional differential has a ratio of torque distribution 50:50 i.e., ratio of torque distribution 1:1 or sometimes 1.5:1, the limited slip differential (FIG. 8) alters this torque distribution in favor of the axle with the greater adhesion or traction to the ratio 80:20 or 4:1 and in some cases 6:1. That is to say, while the free-running wheel is in a condition of spinning and high loss of adhesion or traction loss, the other axle with high traction picks up a small speed and passes to a condition with a higher coefficient of friction.
Because these limited slip differentials use an engagement type between the two output axles, namely a clutch with disks fitted on the output axles, where the speed difference is balanced by the friction forces between the two disks, high friction forces occur resulting in the development of high temperatures and the quick wear of the system.
These limited slip differential systems also do not react promptly and allow the development of significant speed differences between the axles, resulting in the failure to avoid the spinning of the wheel with the lower adhesion or lower traction.
An evolution of these differentials are the differentials with cohesive engagement. In this case, the disks are perforated and special fluid flows through the disks. The balancing of the axle speeds is achieved by the variation of the fluid pressure and subsequently of the friction forces between the disks. The operation characteristics and the engagement time vary with the number of the disks, and the film thickness of the fluid.
The advantage of these differentials, compared to the simple engagement differentials, is their reduced weight and inertia.
The Torsen type differentials are a specific and peculiar planetary gear system. In the center of the system, worm gears form the output towards the axles, while on their perimeter and the inside of the casing three pairs of shafts are fitted with gears meshing with the sun gear disposed on the central axis of the gear train and between the gears.
This Torsen type system has the ability of rapid torque transmission to the axle of the wheel with the greater resistance, i.e. the wheel subjected to greater adhesion and traction. Consequently, the Torsen type system differs from the limited slip differentials, since the Torsen type system has an immediate reaction and does not allow for significant speed differences between the axles and also does not permit a spinning of the wheel exhibiting a lower friction and lower adhesion. The Torsen type system results therefore in an absence of spinning of the wheel accompanied by a lower traction. On the other hand, the Torsen system has problems based on the increased weight and inertia because of the large numbers of gears, and from the high friction levels resulting in wear and creating high temperatures. The ratio of the delivered torque could reach a value of 6:1.
Some of these disadvantages have been reduced by the use of improved metal alloys and a simplification of the system. Features from Patent eqivex are making the Torsen type system lighter and simpler, but it still is at a disadvantage concerning the torque distribution, wherein the ratio of the distributed torques reaches up to 3:1 (FIG. 8).
Finally, with the new RICARDO differential currently under testing, the transmission is not achieved through gears but through a cross disposed and fitted on the differential shaft, wherein the cross is able to slide and rotate simultaneously.
The ball-shaped ends of the cross are properly fitted with disks and are connected with the output axles. In this system, the variation of torque distribution depends not only on the speed difference but also on the load, whose variation, along with the variation of the friction coefficient through the help of an oil film, results in the transmission of a greater torque to the axle with a lower speed.
Tests have shown that the amount of the change of the torque distribution ratio depends on the selected speed ranging from 5:1 up to a minimum of 2:1.